<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<input id="num1" /> + <input id="num2" />
		<input type="button" value="=" onclick="jisuan()" />
		<input id="num3" />
	</head>
	<body>
	<script>
	        var jisuan = function(){
	        	num3.value = parseFloat(num1.value) + parseFloat(num2.value);
	        };
	</script>
	</body>
</html>
